Can it not be so that the dark matter we're looking for perhaps not even exist and the bindimg/repelling force might be space itself, since black holes collide and gravitational waves are generated, and the speed at which those waves travel can't surpass that of light, so it may be that those waves together with other collisions' waves interact for millions of years thus preventing galaxies from falling apart? Could it be that when two waves collide they create anti gravity? i.e., the space in that field starts to contract, like one wave generated by two black holes when collides with another wave generated by two other.